Which effects does consumption of caffeine during workout have?
I usually drink one or two 0.7l bottles of water before, during and after workout. I drink about one or two cans of tea daily, and was wondering if it has a detrimental effect when I keep drinking tea instead of water while working out.
I also noticed that some pulverized energy drinks contain some amount of caffeine and was wondering what the effects of caffeine consumption are on both strength and cardio exercises.

As I regularly drink coffee, tea or mate I am somewhat used to caffeine. Would there be different effects if I'd increase the dose or if someone who isn't used to caffeine would start consuming during exercise?

Caffeine has been proven to have some positive effects on endurance exercise, but in higher amounts than you are drinking, and when the person doesn't regularly consume caffeine. For your case, there wouldn't be much effect unless you cut out caffeine and then dosed before an event. I'm not aware of any positive effects on short burst strength based activities.
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JohnPJan 6 '13 at 15:25

@JohnP If there are negative effects it would be interesting to know, too. Eg caffeine increases the heartbeat, so I wonder if this might just be 'too much' when doing something like HIIT.
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BaarnJan 6 '13 at 15:30

@Chris it is not off topic as it relates to exercise.
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BaarnJan 6 '13 at 18:13

@Informaficker, you misunderstand. The question does relate to exercise, but I was under the impression that questions requiring "List" answers were off topic on this site. Answering the question "What are the short term effects of caffeine" comprehensively requires a list of effects.
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MewJan 7 '13 at 2:23

1 Answer
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Your caffeine consumption, practically speaking, probably does not affect your workouts positively or negatively. As @JohnP pointed out, caffeine studies are on greater amounts than a couple of cans of tea per day. According to the Sports Med. 2001;31(11):785-807, "ingestion of caffeine as coffee appears to be ineffective compared to doping with pure caffeine."

Caffeine has been "shown to increase speed and/or power output in simulated race conditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. "

on strength; however, recent work suggests no effect on maximal ability, but enhanced endurance or resistance to fatigue

Ingesting caffeine reduces muscular pain during exercise in hot but not cold temperatures, This study found that, although caffeine improves exercise capacity, its effect on leg muscle pain is dependent on ambient temperature. Although exercise in the heat increases muscle pain compared to a cooler environment, caffeine reduces this pain.

Negative Effects: According to the American College of Sports Medicine:

The side effects of caffeine ingestion include anxiety, jitters, inability to focus, gastrointestinal unrest, insomnia, irritability, and, with higher doses, the risk of heart arrhythmias and mild hallucinations. While the side effects associated with doses of up to 9 mg/kg do not appear to be dangerous, they can be disconcerting if present prior to a competition and may impair performance.

There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects.

As for whether or not the effects vary depending on if someone consumes caffeine regularly, while this would seem to be the case, and is often said to be the case, I don't have a reference to confirm this.